Uncovering the cornerstones of our Universe: Application and Development of Next-Generation Stellar Atmospheres

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Massive stars and their interaction with the environment are keystones of modern astrophysics. Their influence ranges from the first stars over the chemical evolution of galaxies up to the progenitors of supernovae and gravitational wave events. Despite their importance, the quantitative impact of massive stars is poorly constrained and current descriptions turn out to be insufficient. This significantly blurs our perception of stellar evolution in the upper mass regime and obscures our interpretation of processes crucially dependent on stellar feedback, such as stellar population synthesis or the nature of massive black holes.To constrain and predict the properties of massive stars, such as their spectra, winds, and feedback, proper modelling of their expanding atmospheres is essential. This requires a complex numerical treatment in a non-equilibrium environment, for which the hydrodynamic structure is traditionally approximated by means of an analytical description. However, this description has proven to be insufficient. Especially for evolved stars, significant discrepancies arise between the parameters predicted by stellar evolution and those obtained via model atmospheres. The consequences are fundamental uncertainties in the properties and evolution of massive stars, which can reach orders of magnitude when extrapolating current descriptions to earlier cosmic times. The interpretation of gravitational wave events and the oncoming era of high-redshift astrophysics more than ever rely on a robust knowledge of massive stars and their feedback. Thus, a dangerous gap emerges between our observational capabilities and our theoretical understanding.My Emmy Noether research group aims at closing this gap by focussing on one of the key tools in the field of modern astrophysics: The application and development of stellar atmospheres. My efforts over the past years have paved the way for a new generation of stellar atmospheres, capable of overcoming the limitations of classical approaches by coupling the radiative transfer with consistent hydrodynamics. With this technique, it is possible to capture the full physics inherent to hot star winds and predict the feedback consistently from a given set of stellar parameters. My research group will revise our understanding of radiatively-driven winds and obtain a coherent picture of hot star feedback at different regimes and metallicities, ranging even back to the first stars. With analytical and theoretical applications of next-generation atmospheres, we can trace all relevant stages of hot star evolution and investigate the impact on stellar populations. By coupling atmosphere and structure models, we will establish a new level of consistency in stellar evolution. All of these efforts will be complemented by the constant extension and improvement of the model atmosphere code, which will further be made accessible to the whole astrophysical community.